CuO2 Layers Research Articles

Construction of internally stacked Cu2O:CuO layers in Cu2O:CuO/Gr/ZnO heterojunctions for solar cells applications

The present work shows the construction of CuO grains on the electrodeposited Cu2O layer through annealing method and the photovoltaic effect of Cu2O:CuO/ZnO heterojunctions with graphene buffer layer is also discussed. The annealing temperature of Cu2O layer is varied from 100 to 300 °C. The graphene monolayer was deposited by chemical vapor deposition method. The morphology, structural and electrical properties of Cu2O layer were characterized by using Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray Diffractometry (XRD) and I-V measurement, respectively. The Cu2O grains size increase as the annealing temperature increased and the CuO grains could be observed at 300°C. The graphene monolayer was successfully inserted in between Cu2O:CuO/ZnO heterojunction. The Cu2O:CuO/Gr/ZnO heterojunction shows high electrical rectification with threshold voltage of 0.5 V.

Controlled exposure of CuO thin films through corrosion-protecting, ALD-deposited TiO2 overlayers

Abstract Ultra-thin film coatings are used to protect semiconductor photoelectrodes from the harsh chemical environments common to photoelectrochemical energy conversion. These layers add contact transfer resistance to the interface that can result in a reduction of photoelectrochemical energy conversion efficiency of the photoelectrode. Here, we describe the concept of a partial protection layer, which allows for direct chemical access to a small fraction of the semiconductor underlayer for further functionalization by an electrocatalyst. The rest of the interface remains protected by a stable, inert protection layer. CuO is used as a model system for this scheme. Atomic layer deposition (ALD)-prepared TiO2 layers on CuO thin films prepared from electrodeposited Cu2O allow for the control of interfacial morphology to intentionally expose the CuO underlayer. The ALD-TiO2 overlayer shrinks during crystallization, while Cu2O in the underlayer expands during oxidation. As a result, the TiO2 protection layer cracks to expose the oxidized underlying CuO layer, which can be controlled by preceding thermal oxidation. This work demonstrates a potentially promising strategy for the parallel optimization of photoelectrochemical interfaces for chemical stability and high performance.

In Situ Growth of 3D Lamellar Mn(OH)2 on CuO-Coated Carbon Cloth for Flexible Asymmetric Supercapacitors with a High Working Voltage of 2.4 V

Flexible asymmetric supercapacitor (FASC) systems are expected to exhibit not only excellent energy storage properties and safety but also satisfactory flexibility and robust integration. However, tremendous issues such as low capacitance, narrow voltage window, and poor mechanical properties still exist. In this paper, a novel kind of 3D lamellar Mn(OH)2 nanosheets on Cu-plated carbon cloth with a core-shell integrated framework (CPCC@CuO@Mn(OH)2) is fabricated to obtain the flexible material in the FASC. In this unique CPCC@CuO@Mn(OH)2 electrode material, the high theoretical specific capacity of CuO and Mn(OH)2 brings superior energy storage properties. Meanwhile, as the shell part, the deposited Mn(OH)2 layer and coated CuO layer work as both capacity contributors and substrate protectors, simultaneously maintaining the high capacitance and satisfactory flexibility of the electrodes. Therefore, the capacitance successfully achieves around 8140 mF cm–2 under 0.5 mA cm–2. Significantly, the assembled FASC (named as CPCC@CuO@Mn(OH)2//CC@AC) achieves a working voltage of up to 2.4 V. In the case of a high-power density close to 34.31 mW cm–3, its energy density reaches around 6.29 mW h cm–3. Moreover, the capacity holds 88.9% even after 10,000 cycles, showing its great application potential in the field of wearable electronics.

Unusual metallic conductivity of high-Tc cuprates

The intrinsic mechanisms of the unusual metallic transports of three types of relevant charge carriers (large polarons, excited (dissociated) polaronic components of bosonic Cooper pairs and bosonic Cooper pairs themselves) along the CuO2 layers of high-Tc cuprates are identified and the new features of metallic conductivity in the CuO2 layers (i.e. ab -planes) of underdoped and optimally doped cuprates are explained. The in-plane conductivity of high-Tc cuprates is associated with the metallic transports of such charge carriers at their scattering by lattice vibrations in thin CuO2 layers. The proposed charge transport theory in high-Tc cuprates allows to explain consistently the distinctive features of metallic conductivity and the puzzling experimental data on the temperature dependences of their in-plane resistivity pab. In underdoped and optimally doped cuprates the linear temperature dependence of pab(T) above the pseudogap formation temperature T∗ is associated with the scattering of polaronic carriers at acoustic and optical phonons, while the different (upward and downward) deviations from the linearity in pab(T) below T∗ are caused by the pseudogap effect on the conductivity of the excited Fermi components of bosonic Cooper pairs and by the dominating conductivity of bosonic Cooper pairs themselves in the normal state of these high-Tc materials.

Ultrathin Metals on a Transparent Seed and Application to Infrared Reflectors.

Ultrathin metal films (UTMFs) are widely used in optoelectronic applications, from transparent conductors to photovoltaic cells, low emissivity windows, and plasmonic metasurfaces. During the initial deposition phase, many metals tend to form islands on the receiving substrate rather than a physically connected (percolated) network, which eventually evolves into continuous films as the thickness increases. For example, in the case of Ag and Au on dielectric surfaces, percolation begins when the thickness of the metal film is at least about 5 nm. It is known that the type of growth can be changed when a proper seed layer is used. Here, we show that a CuO layer directly deposited on a substrate can dramatically influence surface wetting and promote early percolation of polycrystalline Ag and Au UTMFs. We demonstrate that the proposed seed is effective even when its thickness is sub-nanometric, in this way maintaining the full transparency of the receiving substrate. The Ag and Au films seeded with CuO showed a percolation thickness close to 1 nm and were morphologically and optically characterized from an ultraviolet (λ = 300 nm) to a midinfrared (λ = 15 μm) wavelength. Infrared reflectors, a mirror and a resonant plasmonic structure, were also demonstrated and uniquely tuned by electrical gating, this being possible owing to the small thickness of the constituting Au UTMF.

Comparative Simulation-Based Study on Different Active Layers of Organic Solar Cell via GPVDM

The high strength of organic photovoltaic cells lies in the variety of organic ingredients that can be built and synthesized for absorbers, receptors, and boundaries. Still, we need further development for better performance and existence of the system. In this research study, electrical simulations of different active layer materials have been performed via GPVDM software to observe the outcomes of a solar cell. Furthermore, the electrical simulation has been performed at different active layer thicknesses from 50 nm to 300 nm with active material P3HT: PC70BM. We analyzed by performing simulations with different parameters to observe the best parameters for organic solar cell performance. We observed that absorber layer thickness of 200 nm, hole transport layer of Cu2O, pair of ITO/Al electrodes, and exponential DOS exhibit superior outcomes. At the same time, the highest power conversion efficiency was reported with active layer PTB7:PCB70BM due to its efficient optical properties. Organic solar cells are versatile and gaining popularity for a broad range of applications to keep up with the increasing energy demand and comparatively lower energy payback time.

Solid‐State Fabrication of Cu2O/CuO Hydroxide Nanoelectrode Array onto Graphene Paper by Thermal Dewetting for High‐Sensitive Detection of Glucose

Nanostructures of Cu2O/CuO hydroxide suitable for the electrochemical determination of glucose are obtained by solid‐state dewetting of CuO layers 6, 8, and 31 nm thin deposited by sputtering onto 240 μm‐thick graphene paper. Solid‐state dewetting in nitrogen produces a partial decomposition of CuO into Cu2O and Cu. X‐ray diffraction patterns reveal the presence of high‐index crystallographic facets, which are reactive and useful toward glucose oxidation to gluconolactone. Typically, morphology studied by scanning electron microscopy reveals faceted nanoparticles with an average size below 200 nm. X‐ray photoelectron spectroscopy shows that the nanostructure surfaces of Cu2O and metallic copper exposed to natural ambient are promptly reoxidized and hydroxidized to a mixture of CuO and Cu(OH)2. Electrochemical characterization in amperometric mode reveals linear response to glucose concentration in the range from 50 to 10 × 10−3 m, sensitivity up to 83 μA cm−2 mm −1, and limit of detection up to 3.6 × 10−6 m. Good combination of low cost and simplicity of preparation with low limit of detection, high sensitivity, and wide linear range makes the proposed electrodes suitable for a variety of applications ranging from health to food and beverage industries.

Galvanic Transformation Dynamics in Heterostructured Nanoparticles

AbstractCorrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). Here, it is shown that bimetallic hetero‐nanostructures composed of phase‐segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half‐spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two‐stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.

Write-once-read-many-times characteristics of CuO layer with Ag conductive bridges

This paper demonstrates write-once-read-many-times (WORM) behavior of an Ag/CuO/n+-Si memory device. The CuO resistive switching layer with a thickness of 9.7 nm was prepared using a sol–gel process. The device shows a low conduction current of 10−10 A at a read voltage of 1 V. A sudden current increase is observed when the voltage increases to ∼3 V, corresponding to a resistance switching from a high-resistance state (HRS) to a low-resistance state (LRS). After that, the device remains in the LRS. Degradation of the HRS and the LRS is not observed for 104 read cycles. The HRS/LRS resistance ratio is 106, and the data retention time is over 105 s. The abrupt current increase cannot be triggered by a negative bias. The formation of Ag conductive bridges in the CuO layer is responsible for the resistance switching. Statistical analyses are performed to study the distributions of the set voltages and the resistances in the HRS and LRS. The effect of the compliance current on the operating current of the Ag/CuO/n+-Si WORM memory is also investigated. The carrier transport mechanisms are found to be dominated by Schottky emission, Ohmic, and SCLC conductions. The energy barrier is 1.066 eV, which is extracted by Schottky emission analysis.

Monolayered graphene oxide as a protective barrier on polycrystalline copper substrate against thermal oxidation for a long duration

This work aimed to describe an innovative and economical method for coating copper with Graphene Oxide (GO) via dip coating and a study of the resulting barrier properties against oxidation. The thickness GO was found as an optimized thin film in the nanometer (0.5–0.7 nm) range. The kinetics of thermal oxidation at low temperature (160 °C) is followed by an original procedure based on Raman spectroscopy. This approach permitted an unambiguous identification of cuprous oxide (Cu2O) on micron size regions and probed the measurement of the thin oxidized layer down to the nm scale. The findings showed that a monolayer of GO does not substantially alter oxidation kinetics at short times (~1 h). Furthermore, it was found that GO film exhibited highly improved thermal oxidation stabilities due to remarkable gas barrier property. It remained an excellent candidate for passivation barrier and resistance to oxidation of copper since GO film significantly reduced the further propagation of the Cu2O layer at a long timescale (days) under the barrier film.

Construction of Bi2WO6 composites with carbon-coated Cu2O for effective degradation of tetracycline

It is of great significance to achieve superior degradation of contaminants by developing efficient and stable photocatalysts. To boost the photocatalytic performance of Bi2WO6 for tetracycline degradation, the Bi2WO6 composites (Bi2WO6/C@Cu2O) were constructed by introducing Cu2O coated by carbon layer (C@Cu2O with 5 wt% of Bi2WO6) in this study. Bi2WO6/C@Cu2O presents an excellent performance on tetracycline degradation because of the generation of more active species as ∙O2- and ∙OH. Its kinetic rate constant k was 2.8 times of pure Bi2WO6 and tetracycline degradation efficiency maintained outstanding stability even after 4 cycles. This benefits from the higher photogenerated charge separation and electron transfer possessed by Bi2WO6/C@Cu2O compared to Bi2WO6. Various intermediates of tetracycline degradation were identified and the possible degradation pathways were proposed. The tetracycline degradation by Bi2WO6/C@Cu2O followed a Z-scheme photocatalysis mechanism. In addition to acting as the protective layer of Cu2O to attenuate the photo-corrosion of Cu2O, the oxygen containing functional groups CO on the surface of carbon layer could provide an electron transfer channel between the interface of Bi2WO6 and Cu2O to reduce the interfacial charge-transfer resistance and accelerate the electron transfer.

Open-air printing of Cu2O thin films with high hole mobility for semitransparent solar harvesters

Cu2O is a promising p-type semiconductor for low-cost photovoltaics and transparent optoelectronics. However, low-cost and low-temperature fabrication of Cu2O films with good transport properties remains challenging, thus limiting their widespread adoption in devices. Here, we report Cu2O thin films of 20–80 nm thickness with hole mobility up to 92 cm2V−1s−1 using atmospheric-pressure spatial atomic layer deposition at temperatures below 260 °C, from a copper (I) hexafluoro-2,4-pentanedionate cyclooctadiene precursor. Raman spectroscopy indicates the presence of copper split vacancies and shows that the high hole mobility can be correlated to a low concentration of shallow acceptor defects. The optical bandgap of deposited films can be tuned between 2.08 eV and 2.5 eV, depending on the deposition temperature. All-oxide semitransparent Cu2O/ZnO solar harvesters are fabricated, showing efficiency values comparable to devices that incorporate much thicker Cu2O layers. Our work provides a promising approach towards cost-efficient, all-oxide solar harvesters, and for other (opto)electronic devices.

Machine-Learning-Guided Prediction Models of Critical Temperature of Cuprates.

Cuprates have been at the center of long debate regarding their superconducting mechanism; therefore, predicting the critical temperatures of cuprates remains elusive. Herein, using machine learning and first-principles calculations, we predict the maximum superconducting transition temperature (Tc,max) of hole-doped cuprates and suggest the functional form for Tc,max with the root-mean-square-error of 3.705 K and R2 of 0.969. We have found that the Bader charge of apical oxygen, the bond strength between apical atoms, and the number of superconducting layers are essential to estimate Tc,max. Furthermore, we predict the Tc,max of hypothetical cuprates generated by replacing apical cations with other elements. Among the hypothetical structures, the cuprates with Ga show the highest predicted Tc,max values, which are 71, 117, and 131 K for one, two, and three CuO2 layers, respectively. These findings suggest that machine learning could guide the design of new high-Tc superconductors in the future.

Antiferromagnetic Order and Spin-Canting Transition in the Corrugated Square Net Compound Cu3(TeO4)(SO4)·H2O.

Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquids, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner-sharing square-planar CuO4 units have been intensely studied due to their Mott insulating ground state, which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid-state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate, Cu3(TeO4)(SO4)·H2O, a promising alternative to layered perovskites. The orthorhombic phase (space group Pnma) is made of corrugated layers of corner-sharing CuO4 square-planar units that are edge-shared with TeO4 units. The layers are linked by slabs of corner-sharing CuO4 and SO4. Using both the bond valence sum analysis and magnetization data, we find purely Cu2+ ions within the layers but a mixed valence of Cu2+/Cu+ between the layers. Cu3(TeO4)(SO4)·H2O undergoes an antiferromagnetic transition at TN = 67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at T* = 12 K, evidenced by a kink in the heat capacity. The spin-canting transition is explained on the basis of a J1-J2 model of magnetic interactions, which is consistent with the slightly different in-plane superexchange paths. We present Cu3(TeO4)(SO4)·H2O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.

Multiferroic and phonon properties at the phase transition of S = 1/2 chain cuprates NaCu2O2. Comparison with LiCu2O2

ABSTRACT The multiferroic properties of NaCuO (NCO) around the phase transition temperature are studied theoretically. The total polarization P is zero without magnetic field h due to the antiferroelectric state induced by the alternate stacking of CuO layer with opposite spin vector chirality. Applying h P increases, goes through a maximum and vanishes at . The magnetic field dependence of is an evidence that NCO is multiferroic. For h = 0 there is no anomaly in the dielectric constant at which is an evidence for the antiferroelectric behavior of the compound. It is observed that and in NCO is quite different compared to that of LiCuO. Around the Neel temperature we observe in NCO an anomaly in the specific heat and the phonon energy due to strong anharmonic spin-phonon interaction. This kink disappears by applying an external magnetic field h.

First-Principles investigation on the behavior of Pt single and triple atoms supported on monolayer CuO (1 1 0) in CO oxidation

CuO layers coated with single noble metal atoms has been used in CO oxidation, but understanding of its mechanism is still ambiguous. A series of first-principles calculations were performed in this study to investigate the properties of a single Pt atom and triple Pt (Pt3) atoms supported on a CuO(110) layer on a Cu(110) substrate and their role in CO oxidation reactions. Calculations on the adsorption energies of O2 and CO2 as well as the subsequent energy evolution revealed that the Pt3 atoms were more active than the single Pt atom in CO oxidation. The catlyts surface with Pt3 atoms was reconstructed by CO oxidation, while no reconstruction phenomenon was found on the surface with the single Pt atom. Further, tensile properties along the [110] and [001] directions elucidated that the weak bonding between the Pt3 atoms and the substrate could result in the surface reconstruction.

Determination of Possible Maximum Critical Transition Temperatures with Empirical Model Depending on Structural Disorders-Defects for Bi2.1Sr2.0Ca1.1Cu2.0Oy System

In this study, we find a strong link depending on the preparation annealing ambient conditions between structural disorders-defects and characteristic transition temperature parameters (offset, Tc offset and onset, Tc onset) of bulk Bi2.1Sr2.0Ca1.1Cu2.0Oy system for the first time. The superconducting samples are prepared at various annealing temperatures intervals 830°C -850°C with the temperature step of 10°C for annealing time ranging between 24 h and 48 h via traditional solid-state reaction route. The temperature-dependent resistivity measurements are conducted at temperature range of 30-140 K. The most ideal annealing ambient is obtained to be the combination of annealing temperature of 840 °C and annealing time of 24 h because of the enhancement in the formation possibility of strong cooper-pairs and optimization of itinerant charge carrier concentrations in the valence band. Similarly, the positive contributions are observed in the overlapping mechanism of wave functions between Cu-3d and O-2p electrons and especially logarithmic distribution of electronic state densities. The optimum annealing ambient makes the Bi-2212 system refine the structural problems and especially connectivity between the grains in the crystal structure. Conversely, the excess annealing ambient leads to increase considerably the grain misorientation, defects and grain boundary couplings due to the induced permanent problems in the crystal system. The highest correlated model shows that the Bi-2212 superconducting compounds with the minimum structural disorders in the short-range-ordered antiferromagnetic Cu-O2 layers exhibit the maximum Tc onset and Tc offset values of about 85.347 K (R2adj=0.9882) and 87.421 K (R2adj=0. 97465).

(Invited) Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

We present a cyclic process for selective and anisotropic atomic layer etching of copper: an oxygen plasma modulates the depth and directionality of the oxidized layer while formic acid vapor selectively removes the copper oxide scale from the metallic copper. Via density functional theory, with finite temperature and pressure free energy corrections, we evaluate the feasibility of formation of gas-phase Cu(II) and Cu(I) complexes with formate, water, formic acid, and combinations thereof as ligands. These complexes result from the neutralization reaction between copper oxide (CuO and Cu2O) and formic acid, with and without water. We identified and evaluated the formation free energies of formato, formic acid, aquahydroxo, and aquaformato complexes of Cu(II) and Cu(I). Under relevant experimental pressures, we find the water-free dimeric tetra(μ-formato)dicopper(II) “paddlewheel” complex (Cu2(HCOO)4) to be the most favorable etching product, with its formation reaching equilibrium conditions from CuO. The most likely precursor for the dimer is the diformatodi(formic acid)copper(II) monomer, which favorably dimerizes under the same water-lean condition at which the dimer persists. Stabilization of gas-phase Cu (oxide) derivatives thus can be achieved through complexation, enabling gas-phase etching of Cu. This work provides complementary experimental and theoretical studies that illuminate the nature of highly controlled etching with formic acid of nanoscopic CuO(s) layers covering Cu nanoarchitectures, which is relevant for the fabrication of next-generation integrated circuits.

Synthesis of SnO2/CuO/SnO2 Multi-layered Structure for Photoabsorption: Compositional and Some Interfacial Structural Studies

Many metal oxide heterostructures have been synthesized as mixed oxides or layered structures for photocatalytic, photodegradation of pollutants and light-harvesting applications. However, in the layered structures the effects of interfacial properties and composition have largely not been explored. Hence, the effects of interfacial mixing and diffusion of sandwiched thin CuO layer on optical absorption of as-deposited and heat-treated multi-layered structured SnO2/CuO/SnO2 films were studied. The RBS analysis of the as-deposited films showed the presence of a minute amount of Cu in the surface and bottom SnO2 layers of the structure. We attributed this to inhomogeneous layer thickness evidenced by very low Sn/Cu atoms ratio of the CuO layer. However, the thermal treatment of the layered structure led to pronounced interlayer mixing and consequent formation of SnO2-CuO solid solutions throughout the layered structure. The layer integrity of the inserted CuO of the as-deposited films was very high and the as-deposited structure was far more optically absorbing. However, the annealed structure showed lesser optical absorption because of the onset of interfacial mixing and improved crystallization. This reflected in the optical bandgap variations of the as-deposited and annealed multilayered structures. The significance of this result is that the multi-layered films possess band narrowing – evidence of increased photon absorption - making it a better candidate than pure SnO2 oxide for photocatalysis, photodegradation and photodetection applications. It also pointed to the fact that attention must be paid to effects of heat treatments or annealing when inserting an absorbing layer into a photocatalyst or a material meant for photodegradation or any light-harvesting material.

CuFe2O4/CuO coating for solid oxide fuel cell steel interconnects

CuFe0.8 (Fe:Cu = 0.8:1, atomic ratio) alloy layer is fabricated on both bare and pre-oxidized SUS 430 steels by direct current magnetron sputtering, followed by exposing at 800 °C in air to obtain a protective coating for solid oxide fuel cell (SOFC) steel interconnects. The CuFe0.8 alloy layer is thermally converted to CuFe2O4/CuO coating, which effectively suppresses the out-migration of Cr. Pre-oxidation treatment not only initially accelerates the formation of CuFe2O4/CuO coating but also further inhibits the Cr and Fe outward diffusion. Suppressing outward diffusion of Cr could improve electrical property of oxide scale and decrease the risk of cathode Cr-poisoning. Blocking out-diffusion of Fe is beneficial to stabilize the CuO layer. After 2520 h oxidation, the scale ASR at 800 °C is 66.9 mΩ cm2 for coated bare steel, 43.4 mΩ cm2 for the coated pre-oxidized steel.